- Too Many Markers! - Google Maps API — Google Developers https://developers.google.com/maps/articles/toomanymarkers
のメモです。
Some applications are required to display a large number of locations or markers. Despite the v3 JavaScript API's significant improvement to performance, naively plotting thousands of markers on a map can quickly lead to a degraded user experience. Too many markers on the map cause both visual overload and sluggish interaction with the map.